Add a "fork" of musl as //fusl.

fusl/src/misc/mntent.c

+#include <stdio.h>
+#include <string.h>
+#include <mntent.h>
+#include <errno.h>
+
+FILE *setmntent(const char *name, const char *mode)
+{
+        return fopen(name, mode);
+}
+
+int endmntent(FILE *f)
+{
+        if (f) fclose(f);
+        return 1;
+}
+
+struct mntent *getmntent_r(FILE *f, struct mntent *mnt, char *linebuf, int buflen)
+{
+        int cnt, n[8];
+
+        mnt->mnt_freq = 0;
+        mnt->mnt_passno = 0;
+
+        do {
+                fgets(linebuf, buflen, f);
+                if (feof(f) || ferror(f)) return 0;
+                if (!strchr(linebuf, '\n')) {
+                        fscanf(f, "%*[^\n]%*[\n]");
+                        errno = ERANGE;
+                        return 0;
+                }
+                cnt = sscanf(linebuf, " %n%*s%n %n%*s%n %n%*s%n %n%*s%n %d %d",
+                        n, n+1, n+2, n+3, n+4, n+5, n+6, n+7,
+                        &mnt->mnt_freq, &mnt->mnt_passno);
+        } while (cnt < 2 || linebuf[n[0]] == '#');
+
+        linebuf[n[1]] = 0;
+        linebuf[n[3]] = 0;
+        linebuf[n[5]] = 0;
+        linebuf[n[7]] = 0;
+
+        mnt->mnt_fsname = linebuf+n[0];
+        mnt->mnt_dir = linebuf+n[2];
+        mnt->mnt_type = linebuf+n[4];
+        mnt->mnt_opts = linebuf+n[6];
+
+        return mnt;
+}
+
+struct mntent *getmntent(FILE *f)
+{
+        static char linebuf[256];
+        static struct mntent mnt;
+        return getmntent_r(f, &mnt, linebuf, sizeof linebuf);
+}
+
+int addmntent(FILE *f, const struct mntent *mnt)
+{
+        if (fseek(f, 0, SEEK_END)) return 1;
+        return fprintf(f, "%s\t%s\t%s\t%s\t%d\t%d\n",
+                mnt->mnt_fsname, mnt->mnt_dir, mnt->mnt_type, mnt->mnt_opts,
+                mnt->mnt_freq, mnt->mnt_passno) < 0;
+}
+
+char *hasmntopt(const struct mntent *mnt, const char *opt)
+{
+        return strstr(mnt->mnt_opts, opt);
+}